AT clone <-rs232-> 3b1 problems

DoN Nichols dnichols at
Sat Jun 15 12:38:49 AEST 1991

In article <1991Jun14.161117.25908 at> alex at (Alex S. Crain) writes:
>	Hey kids!
>	I've been trying to set up a seial link between my at&t 3b1 and
>an Everex AT clone (model 18001) and I'm having trouble.
>	hardware:
>		at&t 3b1, using the stock serial port
>		Everex 18001 with no-name serial card at com1 (8250 driver)
>		Opus PM110 unix coprocessor (optional)
>	Software:
>		kermit/unix3.51 <-> kermit/dos3.31 (no opus card)
>		uucp/unix3.51 <-> uucp/Sys5r3/dos3.31
>	symptoms:
>		The machines connect and pass data for ~20 minutes, at
>		which time the serial card on the AT loses its mind and
>		starts dropping lots of characters (like half). The	
>		system must be rebooted before the card can recover.
>	With marginal effect:
>		Different baud rates: 9600,4800,2400. Slower baud rates
>			take longer to trash the card, but it still happens.

	Sounds like something is counting characters, and failing at a
specific count.

	If it weren't for the fact that this is happening under unix AND
MS-DOS, I would suspect a problem in the BIOS, perhaps one more byte pushed
on the stack than popped off, or vice-versa.  Since the BIOS routines are
not designed to be re-entrant, the unix has to supply its own, so you would
need two parallel problems with the same effect.  (Unless the BIOS is still
counting interrupts from the serial port even while unix is in place.)

	Using something where you can count the characters, like uucp or
kermit, do you have failures at about the same point no matter which way the
files are being transferred.  (Since there are more bytes moving in the
direction the file is going, it should fail first in the direction which
puts the heavier load on the failing software.  If you get failures at about
the same point no matter which direction the file is going, then it is
counting BOTH input and output characters.

	Is it possible that the i/o card has a HARDWARE counter on it?

	Does the opus card run unix UNDER dos?  (In that case, the card may
be running unix, but passing the characters out to dos to send/receive, in
which case the BIOS could be the culprit.)  I'm not familiar with the opus
card, but this seems to be a possibility.

	Good Luck

Donald Nichols (DoN.)		| Voice (Days):	(703) 664-1585
D&D Data			| Voice (Eves):	(703) 938-4564
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	--- Black Holes are where God is dividing by zero ---

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